The present invention relates to a cog rake bar screen used in a wastewater treatment facility, and more particularly to an adjustable pin rack system for use with the cog rake bar screen.
Cog rake bar screens are normally used in municipal and industrial coarse screening applications. The primary purpose of the screens is to retain and remove debris from channeled water flowing into water treatment plants, industrial sites, drainage facilities or overflow control facilities. Usually operated on float controls or timers, the rakers periodically remove debris that has accumulated on the upstream side of a bar screen mounted in the waste stream.
Cog rake bar screens are a front cleaning type of screen mechanism, and typical designs have no moving parts permanently located below the channel water surface. The mechanical cog rakes are guided by a guide track and may, for example, move in a continuous path. Specifically, the cog rake may be lowered along the path and then move upward to remove the debris which has accumulated on the bar screen. After being raised, the cog rake may dump the debris into a trough.
Cog rake bar screens utilize involute gearing and a pin rack system consisting of a series of flat bars, rollers, bushings, pins (bolts), supports, and guides. Driven cog wheels on the motorized drive carriages engage the rollers and bushings of the pin rack system to cause a rake attached to the drive carriage to move along a path defined by the guide track.
Cog rake bar screens are elongated large metal assemblies and require relatively tight design and manufacturing tolerances. During manufacture, all guide tracking is generally shop fit and welded into place inside main side frames. The pin rack system may be shop fit or field installed. The inability of fabrication shops to hold the required tolerances and misalignment resulting from shipping and installation phases of a project cause significant issues. Misalignment and loose tolerances lead to the moving drive carriage and attached rake arm having a tendency to vibrate or pulsate while in operation. If the cog rake bar screens do not run smoothly, then excess vibration causes high stress loading on the sub-assemblies of the main drive carriage which operates within the guide tracks, but can also lead to problems with the engagement of the drive carriage mounted cog wheels as they engage the pin rack system. Excess vibration may also cause the rake arm to lose debris it is attempting to remove.
When components supporting the pin rack system or side frames of the cog rake bar screen are not fabricated to the exact specification, the field personnel and installation contractors are required to shim or grind the screen frames where they meet the pin rack system in order to provide proper cog wheel centerline to centerline spacing and alignment. The practices of shimming and grinding are expensive and time consuming and the overall process involved makes it difficult to provide the required end result. Further, machined blocks currently utilized to support the pin rack system are large, heavy and expensive to fabricate. Attempts to substitute spacers for the blocks do not work, as spacers do not provide proper support of the pin rack system, and allow the pin rack to flex and induce additional vibration of the main drive carriage and rake arm.